Timeing Help!

i just bought a 1990 240sx the kid i bought it off of had tried to do it but really was not mechanicly inclned and messed up the new gasket he put on. so he got frustrated and sold it to me for cheep i replaced the gasket and now im just trying to get some info on the timeing becuase i know theres punch maks on both timeing sprockts, but do u just turn the crank by hand untill the marks line up or do u take the head off and set the timeing right on it and then sent the crank timeing the put the head back on and replace the timeing? any info on timeing or the best way to do it would be great and i would really appriceate it thanks